Effect Of Environmental Factors And The Stress Of Nutrients Deficiency On The Uptake Nitrogen And Chemical Compositions Of Gracilaria Lemaneiformis

The high value of Gracilaria for human food, abalone feed and agar production has led the development of farming systems in the coastal waters in China. This paper examines the growth, N uptake and levels of chemical compositions of G. lemaneiformis under the different indoor conditions. The results showed that temperature and salinity were the major factors influencing growth and ammonium uptake of the seaweed. Light intensity was an important factor regulating the levels of chlorophyll-a, PE and growth rates of the seaweed. With the increase of light intensity from 800³0001x, thegrowth rates of the seaweed increased and Chla & PE increased.Under the 3 nutrient conditions, the special growth rates (SGR) of the seaweed were 0.9% (starvation treatment), 3.06% (control) and 5.01% (add PES), respectively. The tissue elemental contents showed that G lemaneiformis had the higher ratio of total nitrogen (TN) to the lower total carbon (TC) in the experimental group with PES. Whereas the ratio was much lower in the starvation group.The NH₄-N uptake experiments showed that the uptake rates of G. lemaneiformis (the first day of the experiment) were 17.73(starvation treatment), 12.25 (control), and 6.12μmol/g.h.(with PES), respectively. With the increased culture days, the differences of uptake rates decreased gradually among the different treatments, and finally almost same. The highest uptake rate of NO₃-N was only 1.49μmol/g.h. in all experimental treatments which was much lower than that of NH₄-N. This result indicated that G. lemaneiformis assimilate NH4-N first.The grow experiments showed the SGR of G. lemaneiformis were 5.85% (starvation treatment), 5.44% (control), and 5.02% (with PES), respectively. ANOVA analysis indicated that the SGR values werestatistical difference between the starvation treatment and control. The results show that G lemaneiformis owns the characteristics of the over-compensatory growth.Seaweeds have very high productivity and could absorb large quantities of N, P and CO2, produce large amount of O2 and play an excellent role on decreasing eutrophication. In order to improve growth rates of seaweeds in indoor conditions, a photobioreactor was designed. This would be significant for quickly culture of seaweeds in the laboratory scale.